The present invention relates to an electrophotosensitive material used in an image forming apparatus such as a copying machine.
In a recent, image forming apparatus using a so-called Carlson Process, there has been often used, in view of easiness of improvement in sensitivity, a so-called function-separated type photosensitive material in which the charge generating function and the charge transferring function are respectively achieved, as separated from each other, by a charge generating material for generating an electric charge by light irradiation and a charge transferring material for transferring a generated charge. As examples of the function-separated type photosensitive material above-mentioned, there are available (i) a multilayer type photosensitive material in which a multilayer type photosensitive layer unit having a charge generating layer containing the charge generating material and a charge transferring layer containing the charge transferring material, is formed on the surface of a conductive substrate, and (ii) a single-layer type photosensitive material in which a single-layer type photosensitive layer containing both the charge generating material and the charge transferring material, is formed on the surface of a conductive substrate.
Examples of the function-separated type photosensitive material above-mentioned, include (i) an organic photosensitive material in which the entire single-layer type or multilayer type photosensitive layer formed on the surface of the conductive substrate, is an organic layer containing, in a binding resin, functional components such as the charge generating material, the charge transferring material and the like; and (ii) a composite-type photosensitive material in which a portion of the multilayer type photosensitive layer unit is an organic layer. These photosensitive materials above-mentioned are suitably used since they have a variety of choices for materials to be used and present good productivity and high degree of freedom for function designing.
As the binding resin forming the respective organic layers, a variety of synthetic resin materials are used, and polycarbonate excellent in physical properties such as mechanical strength and the like is particularly preferred.
However, the polycarbonate is poor in adhesive properties to the foundation, particularly the surface of the conductive substrate or the like. This presents the problem that the polycarbonate is easily separated while images are continuously formed.
There is the likelihood that the organic photosensitive layer in the organic photosensitive material or the composite-type phtosensitive material becomes fatigued to decrease the charge amount, sensitivity and the like when an image forming process of charging, light exposure, charge eliminating and the like is repeated. To prevent such a problem, there has been recently proposed a photosensitive material in which, in addition to a normal charge transferring material, other charge transferring material of a m-phenylenediamine compound excellent in properties for preventing a decrease in charge amount, sensitivity and the like, is being contained in polycarbonate. There has also been proposed a single-layer type photosensitive material in which polycarbonate contains a m-phenylenediamine compound as the charge transferring material and a perylene compound as the charge generating material.
However, the photosensitive material containing the m-phenylenediamine compound presents the problem of decrease in sensitivity when the photosensitive material is irradiated by light from a fluorescent lamp, a xenon lamp, the sun or the like, particularly at the time when the photosensitive material is heated (usually about 60.degree. C.), for example, during the operation of the image forming apapratus or the like.
On the other hand, when the single-layer type photosensitive material containing both the m-phenylenediamine compound and the perylene compound is irradiated by light from a halogen lamp, the sun or the like while the photosensitive material is under heating, the sensitivity of the photosensitive material is decreased by visible ray contained in the light above-mentioned.